Evidence for actin dual role in regulating chromosome organization and dynamics in yeast

Abstract

Eukaryotic chromosomes undergo movements that are involved in the regulation of functional processes such as DNA repair. To better understand the origin of these movements, we used fluorescence microscopy, image analysis and chromosome conformation capture to quantify the actin contribution to chromosome movements and interactions in budding yeast. We show that both the cytoskeletal and nuclear actin drive local chromosome movements, independently of Csm4, a putative LINC protein. Inhibition of actin polymerization reduces subtelomere dynamics, resulting in more confined territories and enrichment in subtelomeric contacts. Artificial tethering of actin to nuclear pores increased both nuclear pore complex (NPC) and subtelomere motion. Chromosome loci that were positioned away from telomeres exhibited reduced motion in the presence of an actin polymerization inhibitor but were unaffected by the lack of Csm4. We further show that actin was required for locus mobility that was induced by targeting the chromatin-remodeling protein Ino80. Correlated with this, DNA repair by homologous recombination was less efficient. Overall, interphase chromosome dynamics are modulated by the additive effects of cytoskeletal actin through forces mediated by the nuclear envelope and nuclear actin, probably through the function of actin in chromatin-remodeling complexes.

Inferring the physical properties of yeast chromatin through Bayesian analysis of whole nucleus simulations

“…measurements from fixed cells or single snapshots of live cells—we decided to test our model’s ability to predict chromatin dynamics. We therefore compared the mean-squared displacements (MSD) of single loci, predicted by our simulation, to time-lapse microscopy data acquired in three recent studies [64–66] (Additional file 5) (Fig. 5).…”

“…Additional data used for model validation only are: Hi-C data from [62], Micro-C XL data from [63], and chromatin dynamics data from [64–66]. For more details, see Additional file 3 and Additional file 1: Supplementary Methods…”

Keep moving and stay in a good shape to find your homologous recombination partner

“…The same Arp2-3 complex is also the driver of heterochromatic DSB extrusion and perinuclear relocalisation in Drosophila (Caridi et al 2018). Finally, the actin cytoskeleton seems to contribute to chromatin mobility in yeast but its requirement for DSB mobility remains to be tested (Spichal et al 2016). Overall, the conservation of this mechanism in various species plead in favour of its functional relevance for DNA repair.…”

Inappropriate expression of the translation elongation factor 1A disrupts genome stability and metabolism

“…We cannot therefore rule out the possibility that the effects of eEF1A overexpression on spindle organisation and chromosomal segregation are also influenced by a stress response that in turn leads to spindle pole body stabilisation. A role for actin in the regulation of chromosome dynamics in yeast has recently been described in which both cytoplasmic and nuclear actin structures have been implicated (Spichal et al, 2016). An extension of these findings is that stabilisation of actin structures through eEF1A overexpression might alter the dynamic interplay between chromosomes and the nuclear envelope in addition to stabilisation of the spindle pole body.…”